테스트를 위해 수정 불가능한 Go 코드를 어떻게 모의할 수 있나요?

type MyInterface interface {
    DoSomething(i int) error
    DoSomethingElse() ([]int, error)
}

type Concrete struct {
    client *somepackage.Client
}

func (c *Concrete) DoSomething(i int) error {
    return c.client.DoSomething(i)
}

func (c *Concrete) DoSomethingElse() ([]int, error) {
    return c.client.DoSomethingElse()
}

// Mock Concrete
mock := &MockMyInterface{}
c := Concrete{mock}

// Call mock method
err := c.DoSomething(10)

type Concrete struct {
    *somepackage.Client
}

c := Concrete{&somepackage.Client{}}
c.DoSomethingNotNeedingMocking() // Calls the original implementation